Process for alkaline peroxide solution production including alkali concentration control



g- 1969 D. H. GRANGAARD 3,462,351

PROCESS FOR ALKALINE PEROXIDE SOLUTION PRODUCTION INCLUDING ALKALICONCENTRATION CONTROL Filed Jan. 30, 1967 13 4 l4 I0 F /F 7 AL LLL gum/W wig l5 4 3 16 "f --O (AlR) (ANODE) 2 E Q u 51; 1 T T \---|2(CATHODE)United States Patent O US. Cl. 204-83 Claims ABSTRACT OF THE DISCLOSUREThe manufacture of a peroxide containing solution at a controlled andusually low alkalinity by an electrolytic procedure in which the anolyteis provided at a higher alkali concentration than the catholyte.

BACKGROUND OF THE INVENTION Field of the invention This invention isdirected to improvements in the preparation of peroxide bleach solutionsthrough the electrochemical reduction of oxygen. Specifically, theinvention is directed to exercising control over the alkaliconcentration of the caustic solution commonly employed in such cells.

Summary of the invention In brief, particular objects of this inventioninclude the attainment of greater cell efliciency (i.e., gms. or lbs.peroxide/hour) through the medium of higher electrical currents whilemaintaining the caustic concentration of the cathode solution relativelylow. In fact, the alkali concentration of the cathode solution may bedecreased while providing at least the same current flow if theprinciples of the invention are followed. These foregoing and otherobjects, I have found, may be accomplished by cycling through the anodecompartment of the electrolytic cell a caustic solution having aconcentration which is substantially higher than the concentration ofthe caustic solution passed through the cathode compartment. Thesolution passed through the anode compartment may have an alkaliconcentration which is two to five times the concentration of thesolution passed through the cathode compartment. This facilitates theattainment of the above noted objects.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fullyunderstood by reference to the following detailed description andaccompanying drawing wherein the single figure illustratesdiagrammatically one embodiment of a single cell arrangement havingelectrolyte flow paths in accordance with the invention.

PREFERRED EMBODIMENTS OF THE INVENTION Referring to the drawings, thenumeral 1 designates the electrically non-conducting casing of anelectrolytic cell having an anode of nickel designated at 2 and a porousactivated carbon cathode 3. A diaphragm 4 of asbestos separates theanode from the cathode in well spaced relation and inhibits the passageof the anolyte into the catholyte and vice versa. An inlet 5 to thecathode compartment 6 provides for introducing an alkaline elec trolyte(the catholyte) to the cathode compartment 6. An outlet from thiscompartment is designated at 7 and provides for the passage outwardly ofthe alkaline peroxide solution. The anode compartment 8 is suppliedthrough an inlet 9 with an alkaline solution (the anolyte) and an outletport is provided at 10. This anolyte may be recirculated and, due to theprovision of the separate compartments 6 and 8, the concentration ofalkali in the anolyte may differ materially form the concentration ofthe alkali in the catholyte. The anolyte and catholyte flow arerequested so that the electrolyte flow is outwardly from ports 7 and 10and overflow of the cell does not occur. In the schematic diagram shownfor the cell, the necessary oxygen containing gas is introduced throughthe inlet 11 into a chamber 12 serving basically as a manifold forfeeding the gas to the porous cathode 3. Chamber 12 is itself sealedfrom the electrolyte in any convenient manner, as by the contact of thecathode with the casing 1.

The peroxide is formed at the cathode according to the followingequation:

The perhydroxyl then is carried from the cell with the electrolyte,electrolyte flow being indicated by the arrows in the drawing. Also,arrows at 13, 14 indicate the flow of gases involved in the action fromthe cell which at the top is open to the atmopshere, for example.

Specifically, I have found then that, if the alkali concentration of theanolyte is 2 to 5 times the concentration of the alkali in the catholyteand voltage (2 volts) is applied between anode lead 15 and cathode lead16, vastly improved cell efiiciency in terms of grams of peroxideproduced per hour can be obtained without, in turn, appreciablyincreasing the alkali concentration required in the catholyte. This isextremely important since, if the peroxide is to be used for bleachingpurposes, the ratio of peroxide to caustic must be held within rathernarrow limits. Also, it is quite surprising that such occurs so readilyand etficiently since there is electrical conduction or ionic movement,as noted hereinafter, from the compartment 8 of higher alkaliconcentration to the compartment 6 wherein the reaction producing theperhydroxyl takes place.

The improvements in performance obtained through operating a number ofdifferent cell designs in this manner is shown in the following table.

sodium hydroxide. As is known in the art, alkalis, particularlypotassium hydroxide and sodium carbonate, are useful for the samepurpose in generally the same concentrations.

As will be noted from the table above, a very significant increase incurrent and rate of peroxide production occurs simply by increasing thealkali concentration of the anode compartment. Further, theconcentration of the cathode compartment alkali may be beneficiallydecreased if the anolyte concentration is relatively high. Thus, tests Aand B above indicate that by simply increasing the anolyte concentrationto 5%, the cell current and production are increased materially. Tests Cand D show that the reduction of catholyte concentration, whileincreasing the anolyte, is also beneficial.

In these tests the flow rate of the alkali through each compartment isabout the same. Flow rate through the producing compartment 6 is limitedin known manner by the fact that the flow must be sufficiently, slowthat adequate production of the perhydroxyl ion takes place andsufliciently fast that a reasonable quantity of solution containing theion is removed from the cell.

The actual cell construction employed may be in general accordance withthe cell structure shown in my corresponding application, co-filledherewith entitled Process for Producing Peroxide and Electrolytic CellTherefor, Ser. No. 612,515, filed Jan. 30, 1967.

The alkaline solution passed through the inlet and, augmented by theperoxide, exits through outlet 7 and is passed to a bleaching bath or toother usage or storage. A slight increase in alkalinity of the solutionis occasioned by cell operation. The alkaline solution through inlet 9is decreased somewhat in alkali concentration due to movement of thecations through the diaphragm 4 towards the cathode compartment. Thesolution exiting through outlet port 10 thus needs only to berefortified to bring it to the original strength and it may berecirculated through the same cell. If desired in battery operation, theanolyte may be passed from cell to cell.

Data indicate that in usual operation the 5% anolyte solution exits fromthe outlet port '10 at a concentration of about 4.7%. This may varysomewhat with flow rates through the compartment and with the specificnature of the anolyte and electrolyte.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. In a process for the manufacture of an alkaline peroxide solutionwhich includes electrolyzing an aqueous solution of an alkali which isin electrical contact with an anode and a gas porous catalytic cathodeand to the surface of which catalytic cathode an oxygen containing gasis fed, the steps of passing the aqueous electrolyte partment is betweenabout 2 to 5% by weight.

4. A process according to claim 1 wherein the volume rate of how of theanolyte and the catholyte is substantially the same.

5. A process according to claim 4 wherein the anolyte and the catholyteare each selected from the group consisting of aqueous solutions ofsodium hydroxide, potassium hydroxide and sodium carbonate.

References Cited UNITED STATES PATENTS 2,000,815 5/1935 Berl 204-842,297,252 9/ 1942 Schmidt 20484 3,280,014 10/1966 Kordesch et a1. 204-73OTHER REFERENCES The Electrochemical Society, Preprint 76-23, Sept. 14,1939, PP. 281-291.

JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner U.S. Cl.X.R. 204-263

